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• 502 errors with apache mod_proxy hot standby (or equivalent)

  - by 6million

  Anyone knows how to configure the hot standby (+H) mod_proxy feature so that the takeover occurs immediately (without even one user receiving a 502) error during a shutdown? We aren't looking for real load-balancing, we just want a secondary server to take over while we shutdown the primary. The problem is that whenever the primary goes down, I'm able to slip one invalid request resulting in a 502 HTTP error reaching the end user,before the secondary actually takes over. Listen 80 <VirtualHost 127.0.0.1:80> ServerName domain.com ProxyPass / balancer://balance/ <Proxy balancer://balance/> BalancerMember http://primary_ip:80 BalancerMember http://secondary_ip:80 status=+H </Proxy> </VirtualHost>

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• redundant http load balancer

  - by jrydberg

  Got a simple scenario with two web servers for redundancy and to scale. But how do I make a two web-server setup fully redundant? I can think of two solutions; two web servers, one load balancer spreading the load. one extra machine for the load balancer. but how will the load balancer be redundant? two machines, each running the web server AND running a load balancer, spreading the load over. have a DNS entry point to both of the machines. no extra machines needed for load balancing. How do you guys normally solve this kind of problem?

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• Single web app, multiple web servers

  - by Ramakrishna

  I have a problem of load balancing. We developed a web app for nearly 1500 users. As the number of users increased we are unable to serve the requests in a timely manner. It takes around 10 to 20 seconds to load a page. Under heavy load it can take one minute to serve the page. We need to solve this situation so that each request is served in 2 or 3 seconds. App develped in : asp.net Hosted in : IIS 7.5 Machine configuration : Windows Server 2008, 8GB RAM, 1Mbps bandwidth

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• How is load balancing in big systems implemented?

  - by uther-lightbringer

  Hello, I'm wondering how is implemented load balancing in realy big applications like google or facebook. I know that in normal scenario there may be machine dedicated to this task, but I would like to know how is it resolved in realy big aplication with hundreds of thousans people accessing it in any given time. I am just wondering how exactly when one types google.com will that request find its way to concrete computer (are there multiple load balancers? and how is it set up and implemented that user's request will find the way to concrete balancer out of many others). I will realy appreciate if someone enlightens me this issue, thank you.

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• how to design pound -> varnish -> jboss for ha + loadbalancing

  - by andreash

  Hello, I'm planning a new infrastructure for our web application. We have two JBossAS5 servers, running in a cluster. Session state will be replicated via JBoss Cache. In front of that, there should be some cache, to speed up delivery of static elements. However, most of the traffic to our app will be via HTTPS. So far, I had been thinking of two Varnish caches in front of the JBossASs, each being configured for loadbalancing to the two JBossASs via round-robin. Since Varnish doesn't handle HTTPS, then there would need to be two pound proxies in front of the Varnishs, dealing with the HTTPS. The two pounds would be made high-available with Heartbeat/LinuxHA. The traffic to www.example.com would then be going through our firewall, from there to the virtual IP of the pounds, from there to the Varnishs, and from there to the JBossASs. Question 1: Does this make sense? Or is it overly complicated, and the same goal can be reached with simpler methods? Question 2: If my layout is fine, how do I configure the pound - Varnish step? Should I a) make the Varnish service high-available through Heartbeat/LinuxHA as well and direct traffic from pound to the virtual IP of the Varnishs, or should I rather b) Configure two independent Varnishs and use load-balancing in pound to address the different Varnishs? Thanks a lot for your insight! Andreas.

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• Haproxy ACL for balance on URL request

  - by Elgreco08

  I'm usung Ubuntu with haproxy 1.4.13 version. Its load balancing two subdomains: app1.domain.com app2.domain.com now i want to be able to use ACL to send based on url request to the right backends For example: http://app1.domain.com/path/games/index.php sould be send to backend1 http://app1.domain.com/path/photos/index.php should be send to backend2 http://app2.domain.com/path/mail/index.php sould be send to backend3 http://app2.domain.com/path/wazap/index.php should be send to backend4 i did used the code the the following acl frontend http-farm bind 0.0.0.0:80 acl app1web hdr_beg(host) -i app1 # for http://app1.domain.com acl app2web hdr_beg(host) -i app2 # for http://app2.domain.com acl msg-url-1 url_reg ^\/path/games/.* acl msg-url-2 url_reg ^\/path/photos/.* acl msg-url-3 url_reg ^\/path/mail/.* acl msg-url-4 url_reg ^\/path/wazap/.* use_backend games if msg-url-1 app1web use_backend photos if msg-url-2 app2web use_backend mail if ..... backend games option httpchk GET /alive.php HTTP/1.1\r\nHost:\ app1.domain.com option forwardfor balance roundrobin server appsrv-1 192.168.1.10:80 check inter 2000 fall 3 server appsrv-2 192.168.1.11:80 check inter 2000 fall 3 backend photos option httpchk GET /alive.php HTTP/1.1\r\nHost:\ app2.domain.com option forwardfor balance roundrobin server appsrv-1 192.168.1.13:80 check inter 2000 fall 3 server appsrv-2 192.168.1.14:80 check inter 2000 fall 3 .... Since the path mail, photos...etc will be application pools on iis, i want to monitor them if they are alive, if the pool does not respond it should stop serving it. my problem is for sure in the regular expression in the ACL acl msg-url-4 url_reg ^\/path/wazap/.* What should i change in the ACL to make it work ? thanks for any hints

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• Load balanced IIS. Should I use NLB, or linux-based reverse proxy, or something else?

  - by growse

  What would be the best approach for load-balancing at least 2-3 Windows 2008 R2 IIS webservers running a multitude of .NET applications? My choices appear to be: 1) Hardware-based network device load balancer, like a Cisco CSS 2) Windows NLB 3) Some sort of linux based proxy, either haproxy or other The three servers sit as VMs on a vSphere farm, so I have the ability to clone to up the instance count in times of high load. I control the switch that the vSphere hosts are plugged into (Cisco 3750), but don't control the switching/routing infrastructure beyond that to the clients. (1) Is too expensive, and probably overkill for my needs. I've included this in case someone figures out a cunning way to do it on my existing network kit, which I doubt. (2) would seem to be the obvious "built-in" option, but seems to be quite fiddly messing around with network interfaces, multicast, and generally other things that seem to be needlessly complex. It's also fairly stupid, in that it can't remove hosts from the pool if they start throwing 500 errors or otherwise go wrong (3) is the most interesting option, as it would appear to offer the most flexibility and customizability, but without having to mess around with the network. However, while I'm familiar with the reverse-proxy capabilities of lighttpd etc, I'm not that well read on other options like HAProxy, which might be able to offer a lot more. Which would you go for, and is there anything I've not thought of?

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• How many reverse proxies (nginx, haproxy) is too many?

  - by Alysum

  I'm setting up a HA (high availability) cluster using nginx, haproxy & apache. I've been reading great things about nginx and haproxy. People tend to choose one or the other but I like both. Haproxy is more flexible for load balancing than nginx's simple round robin (even with the upstream-fair patch). But I'd like to keep nginx for redirecting non-https to https among other things right at the point of entry to the cluster. On the other hand, nginx is a lot faster for serving static contents and would reduce the load on the powerful apache which loves to eat a lot of RAM! Here is my planned setup: Load balancer: nginx listens on port 80/443 and proxy_forwards to haproxy on 8080 on the same server to load balance between the multiple nodes. Nodes: nginx on the node listens to requests coming from haproxy on 8080, if the content is static, serve it. But if it's a backend script (in my case PHP), proxy forward to apache2 on the same node server listenning on a different port number. Technically this setup works but my concerns are whether having the requests going through several proxies is going to slow down requests? Most of the requests will be PHP requests as the backends are services (which means groing from nginx - haproxy - nginx - apache). Thoughts? Cheers

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• how to go about scaling a web-application ?

  - by phoenix24

  for someone whoes been primarily a web-application developer, and know not much about scaling/scalability techniques. I'll start by stating my application is written in Python, using Django; a fairly standard setup. I currently use Apache 2.2 for my webserver, and MySql for my database server; both running on the same vps server. Up until now, it was basically a prototype and merely 15-30 concurrent users at any given time; so I had no issues, but now since we'll be adding more users we'll have severe performance issues. So my question is how do i go about scaling my web-application? and my plan is as follows. Now I have just one vps server running, apache + mysql. Next, I plan to add another vps server, to run only MySql; so i'll have one web-server and one db server. Next, I'll add Memcache to the webserver for caching data; and taking some load off mysql. Next, another web-server for serving all the static content; Next, a vps server for load-balancing (nginx/varnish) behind which would be my two web-servers and then db-server. Does that sound like a workable strategy, please guide me around here.

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• How can I use HAproxy with SSL and get X-Forwarded-For headers AND tell PHP that SSL is in use?

  - by Josh

  I have the following setup: (internet) ---> [ pfSense Box ] /-> [ Apache / PHP server ] [running HAproxy] --+--> [ Apache / PHP server ] +--> [ Apache / PHP server ] \-> [ Apache / PHP server ] For HTTP requests this works great, requests are distributed to my Apache servers just fine. For SSL requests, I had HAproxy distributing the requests using TCP load balancing, and it worked however since HAproxy didn't act as a proxy, it didn't add the X-Forwarded-For HTTP header, and the Apache / PHP servers didn't know the client's real IP address. So, I added stunnel in front of HAproxy, reading that stunnel could add the X-Forwarded-For HTTP header. However, the package which I could install into pfSense does not add this header... also, this apparently kills my ability to use KeepAlive requests, which I would really like to keep. But the biggest issue which killed that idea was that stunnel converted the HTTPS requests into plain HTTP requests, so PHP didn't know that SSL was enabled and tried to redirect to the SSL site. How can I use HAproxy to load balance across a number of SSL servers, allowing those servers to both know the client's IP address and know that SSL is in use? And if possible, how can I do it on my pfSense server? Or should I drop all this and just use nginx?

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• F5 BIG_IP persistence iRules applied but not affecting selected member

  - by zoli

  I have a virtual server. I have 2 iRules (see below) assigned to it as resources. From the server log it looks like that the rules are running and they select the correct member from the pool after persisting the session (as far as I can tell based on my log messages), but the requests are ultimately directed to somewhere else. Here's how both rules look like: when HTTP_RESPONSE { set sessionId [HTTP::header X-SessionId] if {$sessionId ne ""} { persist add uie $sessionId 3600 log local0.debug "Session persisted: <$sessionId> to <[persist lookup uie $sessionId]>" } } when HTTP_REQUEST { set sessionId [findstr [HTTP::path] "/session/" 9 /] if {$sessionId ne ""} { persist uie $sessionId set persistValue [persist lookup uie $sessionId] log local0.debug "Found persistence key <$sessionId> : <$persistValue>" } } According to the log messages from the rules, the proper balancer members are selected. Note: the two rules can not conflict, they are looking for different things in the path. Those two things never appear in the same path. Notes about the server: * The default load balancing method is RR. * There is no persistence profile assigned to the virtual server. I'm wondering if this should be adequate to enable the persistence, or alternatively, do I have to combine the 2 rules and create a persistence profile with them for the virtual server? Or is there something else that I have missed?

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• Cisco configuration for public library internet

  - by AlternateZ

  I'm a C/C++ computer programmer turned IT support guy working for a public library. My day is usually spent helping random grandparents learn how to use email, so my networking knowledge is limited to what I can glean from google. Here's the situation. We have a public library with 20 PCs on a LAN and also public wifi access. Previously we were running all of this on 1 ADSL connection and people complained about low speeds. We hired a networking company to set up a Cisco dual-WAN router for us, and purchased an additional ADSL connection. The intention was to give the LAN PCs a guaranteed amount of bandwidth each, and then let the wifi users split the rest. The results were far worse than what we expected, and all we got from the company was excuses and they've since washed their hands of us. During busy periods, net performance on the LAN PCs are so poor that attaching files to gmail etc often times out and fails - far from the "guaranteed amount of bandwidth each" that we hope for! Sometimes it feels like performance is worse than before when we had 1 ADSL link and an unconfigured router? Anyways, surely this is a problem encountered a million times over across the world? (Sharing internet across many users effectively.) What are standard solutions for something like this? I admit to not even knowing the right jargon to google for (load balancing?) I'd appreciate any links to resources/guides that might help me get a better understanding of the problem/solutions, and perhaps some stories of your own experience in solving similar problems. This will help us evaluate and negotiate with network consultants in the future. If its relevant, our router config contains a section "policy-map" with "bandwidth percent" for each class of user (LAN, wifi), and "fair queue".

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• Apache load balancer with https real servers and client certificates

  - by Jack Scheible

  Our network requirements state that ALL network traffic must be encrypted. The network configuration looks like this: ------------ /-- https --> | server 1 | / ------------ |------------| |---------------|/ ------------ | Client | --- https --> | Load Balancer | ---- https --> | server 2 | |------------| |---------------|\ ------------ \ ------------ \-- https --> | server 3 | ------------ And it has to pass client certificates. I've got a config that can do load balancing with in-the-clear real servers: <VirtualHost *:8666> DocumentRoot "/usr/local/apache/ssl_html" ServerName vmbigip1 ServerAdmin [email protected] DirectoryIndex index.html <Proxy *> Order deny,allow Allow from all </Proxy> SSLEngine on SSLProxyEngine On SSLCertificateFile /usr/local/apache/conf/server.crt SSLCertificateKeyFile /usr/local/apache/conf/server.key <Proxy balancer://mycluster> BalancerMember http://1.2.3.1:80 BalancerMember http://1.2.3.2:80 # technically we aren't blocking anyone, but could here Order Deny,Allow Deny from none Allow from all # Load Balancer Settings # A simple Round Robin load balancer. ProxySet lbmethod=byrequests </Proxy> # balancer-manager # This tool is built into the mod_proxy_balancer module allows you # to do simple mods to the balanced group via a gui web interface. <Location /balancer-manager> SetHandler balancer-manager Order deny,allow Allow from all </Location> ProxyRequests Off ProxyPreserveHost On # Point of Balance # Allows you to explicitly name the location in the site to be # balanced, here we will balance "/" or everything in the site. ProxyPass /balancer-manager ! ProxyPass / balancer://mycluster/ stickysession=JSESSIONID </VirtualHost> What I need is for the servers in my load balancer to be BalancerMember https://1.2.3.1:443 BalancerMember https://1.2.3.2:443 But that does not work. I get SSL negotiation errors. Even when I do get that to work, I will need to pass client certificates. Any help would be appreciated.

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• Load balance to proxies

  - by LoveRight

  I have installed several proxy programs whose IP addresses are, for example, 127.0.0.1:8580(use http), 127.0.0.1:9050(use socks5). You may regrard them as Tor and its alternatives. You know, certain proxy programs are faster than others at times, while at other times, they would be slower. The Firefox add-in, AutoProxy and FoxyProxy Standard, can define a list of rules such as any urls matching the pattern *.google.com should be proxied to 127.0.0.1:8580 using socks5 protocol. But the rule is "static". I want *.google.com to be proxied to the fastest proxy, no matter which one. I think that is kind of load balancing. I thought I could set a rule that direct request of *.google.com to the address the load balancer listens, and the load balancer forwards the request to the fastest real proxy. I notice that tor uses socks5 protocol and some other applications use http. I feel confused that which protocol should the load balancer use. I also start to wonder about the feasibility of this solution. Any suggestions? My operating system is Windows 7 x64.

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• 3 Server, is this a cluster scenario?

  - by HornedBeast

  Hello, At the moment I have one Ubuntu server, 9.10, running with a simple Samba share, a mail server, DNS server and DHCP server. Mostly its just there for file sharing and email server. I also have 2 other servers that are exactly the same hardware and spec as the first, which have an rsync set up to retrieve the shared folders and backs them up. However, if the first server goes down, all of our shares disappear along with our mail and the system must be rebuilt. Also I tend to find if people are downloading a large amount from the file server, no-one can access there emails - especially in the morning when everyone is signing in at once. Would it be more beneficial for me to have all 3 servers, all running the same services, doing the same thing with some sort of cluster with load balancing? In short, how can I get the best out of my 3 hardware servers? I'm not really sure where to begin looking, or how to go about such a setup where 3 servers are all identical, but perhaps one acts as the main load balancer?? If someone can point me in the right direction, or if this simply sounds like one of those Enterprise Cloud's that is now a default setup in Ubuntu Server 9.10+, then I'll go down that route. Cheers in advance. Andy

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• How to make Nginx fire 504 immediately is server is not available?

  - by Georgiy Ivankin

  I have Nginx set up as a load balancer with cookie-based stickiness. The logic is: If the cookie is NOT there, use round-robbing to choose a server from cluster. If the cookie is there, go to the server that is associated with the cookie value. Server is then responsible for setting the cookie. What I want to add is this: If the cookie is there, but server is down, fallback to round-robbing step to choose next available server. So actually I have load balancing and want to add failover support on top of it. I have managed to do that with the help of error_page directive, but it doesn't work as I expected it to. The problem: 504 (and the fallback associated with it) fires only after 30s timeout even if the server is not physically available. So what I want Nginx to do is fire a 504 (or any other error, doesn't matter) immediately (I suppose this means: when TCP connection fails). This is the behavior we can see in browsers: if we go directly to server when it is down, browser immediately tells us that it can't connect. Moreover, Nginx seems to be doing this for 502 error: if I intentionally misconfigure my servers, Nginx fires 502 immediately. Configuration (stripped down to basics): http { upstream my_cluster { server 192.168.73.210:1337; server 192.168.73.210:1338; } map $cookie_myCookie $http_sticky_backend { default 0; value1 192.168.73.210:1337; value2 192.168.73.210:1338; } server { listen 8080; location @fallback { proxy_pass http://my_cluster; } location / { error_page 504 = @fallback; # Create a map of choices # see https://gist.github.com/jrom/1760790 set $test HTTP; if ($http_sticky_backend) { set $test "${test}-STICKY"; } if ($test = HTTP-STICKY) { proxy_pass http://$http_sticky_backend$uri?$args; break; } if ($test = HTTP) { proxy_pass http://my_cluster; break; } return 500 "Misconfiguration"; } } } Disclaimer: I am pretty far from systems administration of any kind, so there may be some basics that I miss here. EDIT: I'm interested in solution with standard free version of Nginx, not Nginx Plus. Thanks.

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• apache tomcat loadbalancing clustering on ubuntu

  - by user740010

  i am facing a problem in clustering the tomcat with apache as a loadbalancer using mod_jk on ubuntu. i have install apache2 on my ubuntu 11.04 and i have downloaded tomcat7 created two copies and kept them at two different location. 1st one is at /home/net4u/vishal/test/tomcatA 2nd one is at /home/net4u/vishal/test1/tomcatB i have made following changes to server.xml file in /conf folder 1. <Server port="8205" shutdown="SHUTDOWN"> 2. <Connector port="8280" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> 3.<Connector port="8209" protocol="AJP/1.3" redirectPort="8443" /> <Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcatB"> 4. <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/> similarly i have modified other tomcat i.e tomcatA server.xml content of the server.xml is as follow: -- <!--The connectors can use a shared executor, you can define one or more named thread pools--> <!-- <Executor name="tomcatThreadPool" namePrefix="catalina-exec-" maxThreads="150" minSpareThreads="4"/> --> <!-- A "Connector" represents an endpoint by which requests are received and responses are returned. Documentation at : Java HTTP Connector: /docs/config/http.html (blocking & non-blocking) Java AJP Connector: /docs/config/ajp.html APR (HTTP/AJP) Connector: /docs/apr.html Define a non-SSL HTTP/1.1 Connector on port 8080 --> <Connector port="8280" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <!-- A "Connector" using the shared thread pool--> <!-- <Connector executor="tomcatThreadPool" port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> --> <!-- Define a SSL HTTP/1.1 Connector on port 8443 This connector uses the JSSE configuration, when using APR, the connector should be using the OpenSSL style configuration described in the APR documentation --> <!-- <Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true" maxThreads="150" scheme="https" secure="true" clientAuth="false" sslProtocol="TLS" /> --> <!-- Define an AJP 1.3 Connector on port 8009 --> <Connector port="8109" protocol="AJP/1.3" redirectPort="8443" /> <!-- An Engine represents the entry point (within Catalina) that processes every request. The Engine implementation for Tomcat stand alone analyzes the HTTP headers included with the request, and passes them on to the appropriate Host (virtual host). Documentation at /docs/config/engine.html --> <!-- You should set jvmRoute to support load-balancing via AJP ie : <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm1"> --> <Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcatB"> <!--For clustering, please take a look at documentation at: /docs/cluster-howto.html (simple how to) /docs/config/cluster.html (reference documentation) --> <!-- uncomment for clustering--> <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/> <!-- Use the LockOutRealm to prevent attempts to guess user passwords via a brute-force attack --> <Realm className="org.apache.catalina.realm.LockOutRealm"> <!-- This Realm uses the UserDatabase configured in the global JNDI resources under the key "UserDatabase". Any edits that are performed against this UserDatabase are immediately available for use by the Realm. --> <Realm className="org.apache.catalina.realm.UserDatabaseRealm" resourceName="UserDatabase"/> </Realm> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> <!-- SingleSignOn valve, share authentication between web applications Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> --> <!-- Access log processes all example. Documentation at: /docs/config/valve.html Note: The pattern used is equivalent to using pattern="common" --> <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log." suffix=".txt" pattern="%h %l %u %t &quot;%r&quot; %s %b" resolveHosts="false"/> </Host> </Engine> i have install libapache2-mod-jk step 1. i have Created jk.load file in /etc/apache2/mods-enabled/jk.load content is as follows: LoadModule jk_module /usr/lib/apache2/modules/mod_jk.so Create /etc/apache2/mods-enabled/jk.conf: JkWorkersFile /etc/apache2/workers.properties JkLogFile /var/log/apache2/jk.log JkMount /ecommerce/* worker1 JkMount /images/* worker1 JkMount /content/* worker1 step 2. Created workers.properties file in /etc/apache2/workers.properties content is as follows: workers.tomcat_home=/home/vishal/Desktop/test/tomcatA workers.java_home=/usr/lib/jvm/default-java ps=/ worker.list=tomcatA,tomcatB,loadbalancer   worker.tomcatA.port=8109 worker.tomcatA.host=localhost worker.tomcatA.type=ajp13 worker.tomcatA.lbfactor=1   worker.tomcatB.port=8209 worker.tomcatB.host=localhost worker.tomcatB.type=ajp13 worker.tomcatB.lbfactor=1 worker.loadbalancer.type=lb worker.loadbalancer.balanced_workers=tomcatA,tomcatB worker.loadbalancer.sticky_session=1 i tried the same thing on the windows machine it is working.

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• How can I disable keep-alive on ASP.NET Web Service client requests?

  - by Matthew Brindley

  I have a few web servers behind an Amazon EC2 load balancer. I'm using TCP balancing on port 80 (rather than HTTP balancing). I have a client polling a Web Service (running on all web servers) for new items every few seconds. However, the client seems to stay connected to one server and polls that same server each time. I've tried using ServicePointManager to disable KeepAlive, but that didn't change anything. The outgoing connection still had its "connection: keep-alive" HTTP header, and the server kept the TCP connection open. I've also tried adding an override of GetWebRequest to the proxy class created by VS, which inherits from SoapHttpClientProtocol, but I still see the keep-alive header. If I kill the client's process and restart, it'll connect to a new server via the load balancer, but it'll continue polling that new server forever. Is there a way to force it to connect to a random server each time? I want the load from the one client to be spread across all of the web servers. The client is written in C# (as is the server) and uses a Web Reference (not a Service Reference), which points to the load balancer.

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• "Work stealing" vs. "Work shrugging (tm)"?

  - by John

  Why is it that I can find lots of information on "work stealing" and nothing on a "work shrugging(tm)" as a load-balancing strategy? I am surprised because work-stealing seems to me to have an inherent weakness when implementating efficient fine-grained load-balancing. Vis:- Relying on consumer processors to implement distribution (by actively stealing) begs the question of what these processors do when they find no work? None of the work-stealing references and implementations I have come across so far address this issue satisfactorarily for me. They either:- 1) Manage not to disclose what they do with idle processors! [Cilk] (?anyone know?) 2) Have all idle processors sleep and wake periodically and scatter messages to the four winds to see if any work has arrived [e.g. JAWS] (= way too latent & inefficient for me). 3) Assume that it is acceptable to have processors "spinning" looking for work ( = non-starter for me!) Unless anyone thinks there is a solution for this I will move on to consider a "Work Shrugging(tm)" strategy. Having the task-producing processor distribute excess load seems to me inherently capable of a much more efficient implementation. However a quick google didn't show up anything under the heading of "Work Shrugging" so any pointers to prior-art would be welcome. tx Tags I would have added if I was allowed to [work-stealing]

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• Systems design question: DB connection management in load-balanced n-tier

  - by aoven

  I'm wondering about the best approach to designing a DB connection manager for a load-balanced n-tier system. Classic n-tier looks like this: Client -> BusinessServer -> DBServer A load-balancing solution as I see it would then look like this: +--> ... +--+ +--> BusinessServer +--+--> SessionServer --+ Client -> Gateway --+--> BusinessServer +--| +--> DBServer +--> BusinessServer +--+--------------------+ +--> ... +--+ As pictured, the business server component is being load-balanced via multiple instances, and a hardware gateway is distributing the load among them. Session server probably needs to be situated outside the load-balancing array, because it manages state, which mustn't be duplicated. Barring any major errors in design so far, what is the best way to implement DB connection management? I've come up with a couple of options, but there may be others I'm not aware of: Introduce a new Broker component between the DBServer and the other components and let it handle the DB connections. The upside is that all the connections can be managed from a single point, which is very convenient. The downside is that now there is an additional "single point of failure" in the system. Other components must go through it for every request that involves DB in some way, which also makes this a bottleneck. Move the DB connection management into BusinessServer and SessionServer components and let each handle its own DB connections. The upside is that there is no additional "single point of failure" or bottleneck components. The downside is that there is also no control over possible conflicts and deadlocks apart from what DBServer itself can provide. What else can be done? FWIW: Technology is .NET, but none of the vendor-specific stacks are used (e.g. no WCF, MSMQ or the like).

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• Using Network load balancing to distribute load for SharePoint2010 – Part3 of building my own development SharePoint2010 Farm

  - by ybbest

  Part1 of building my own development SharePoint2010 Farm Part2 of building my own development SharePoint2010 Farm Part3 of building my own development SharePoint2010 Farm In my last post, I have installed SharePoint2010 in one of the server (WFE One) and configured using the OOB SharePoint configuration wizard. In this post I will show you how to use OOB windows network load balancing to distribute load for SharePoint2010 site. 1. Install SharePoint in another server WFE Two (you can follow the steps in my last post), but instead of choosing create new Farm, you need to select “connect to existing farm” this time. 2. Click next then click retrieve database names button and select the farm configuration database. 3. Click next and enter the passphrase you specified when you first installed the SharePoint Farm. 4. Click the advanced settings and select Use this machine to host the web site. 5. Click OK to finish the configurations 6. Next, Install NLB in the two WFE (web front end) SharePoint servers 7. Configure NLB to create the cluster. Go to Start—Administrative Tools—Network Load Balancing Manager 8. Right-click the Network Load Balancing Clusters Node and select New Cluster. 9. Type in the host name that is to be part of the new cluster. 10. Type in the IP address for the cluster. 11. Select the Multicast for this cluster.(The default one is Unicast) 12. You can configure the Port Rules for the clustering , but I will leave the default here. 13. Add another WEF to the cluster. 14. Type in the host name that is to be part of the new cluster. 15. Set the Priority to 2. 16. Click Next to complete the cluster setup. 17. Create an entry in the DNS for the new cluster. 18. Add the binding to the IIS site in the IIS Manager 19. Change the Alternate access mapping for you default site collection from http://sp2010wefone to http://team 20. Browse to http://Team , you will be redirected to the SharePoint site.

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• HAProxy reqrep remove URI on backend request

  - by Jim

  real quick question regarding HAProxy reqrep. I am trying to rewrite/replace the request that gets sent to the backend. I have the following example domain and URIs http://domain/web1 http://domain/web2 I want web1 to go to backend webfarm1, and web2 to go to webfarm2. Currently this does happen. However I want to strip off the web1 or web2 URI when the request is sent to the backend. Here is my haproxy.cfg frontend webVIP_80 mode http bind :80 #acl routing to backend acl web1_path path_beg /web1 acl web2_path path_beg /web2 #which backend use_backend webfarm1 if web1_path use_backend webfarm2 if web2_path default_backend webfarm1 backend webfarm1 mode http reqrep ^([^\ ]*)\ /web1/(.*) \1\ /\2 balance roundrobin option httpchk HEAD /index HTTP/1.1\r\nHost:\ example.com server webtest1 10.0.0.10:80 weight 5 check slowstart 5000ms server webtest2 10.0.0.20:80 weight 5 check slowstart 5000ms backend webfarm2 mode http reqrep ^([^\ ]*)\ /web2/(.*) \1\ /\2 balance roundrobin option httpchk HEAD /index HTTP/1.1\r\nHost:\ example.com server webtest1-farm2 10.0.0.110:80 weight 5 check slowstart 5000ms server webtest2-farm2 10.0.0.120:80 weight 5 check slowstart 5000ms If I go to http://domain/web1 or http://domain/web2 I see it in the error logs that the request on a server in each backend that the requst is for the resource /web1 or /web2 respectively. Therefore I believe there to be something wrong with my regular expression, even though I copied and pasted it from the Documentation. http://code.google.com/p/haproxy-docs/wiki/reqrep Summary: I'm trying to route traffic based on URI, however I want to strip the URI on the backend side. Go to http://domain/web1 -- backend request of / to webfarm1 Thank you! -Jim

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• HAProxy error: Some configuration options require full privileges, so global.uid cannot be changed

  - by Athena Wisdom

  After adding the line to /etc/haproxy/haproxy.cfg as part of creating a transparent proxy, source 0.0.0.0 usesrc clientip restarting haproxy starts giving an error ~# service haproxy reload * Reloading haproxy haproxy [ALERT] 230/153724 (1140) : [/usr/sbin/haproxy.main()] Some configuration options require full privileges, so global.uid cannot be changed. I'm already running service haproxy reload as root. What else do we have to do? Thank you!

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• Apache load balancer limits with Tomcat over AJP

  - by PAS

  Hi All, I have Apache acting as a load balancer in front of 3 Tomcat servers. Occasionally, Apache returns 503 responses, which I would like to remove completely. All 4 servers are not under significant load in terms of CPU, memory, or disk, so I am a little unsure what is reaching it's limits or why. 503s are returned when all workers are in error state - whatever that means. Here are the details: Apache config: <IfModule mpm_prefork_module> StartServers 30 MinSpareServers 30 MaxSpareServers 60 MaxClients 200 MaxRequestsPerChild 1000 </IfModule> ... <Proxy *> AddDefaultCharset Off Order deny,allow Allow from all </Proxy> # Tomcat HA cluster <Proxy balancer://mycluster> BalancerMember ajp://10.176.201.9:8009 keepalive=On retry=1 timeout=1 ping=1 BalancerMember ajp://10.176.201.10:8009 keepalive=On retry=1 timeout=1 ping=1 BalancerMember ajp://10.176.219.168:8009 keepalive=On retry=1 timeout=1 ping=1 </Proxy> # Passes thru track. or api. ProxyPreserveHost On ProxyStatus On # Original tracker ProxyPass /m balancer://mycluster/m ProxyPassReverse /m balancer://mycluster/m Tomcat config: <Server port="8005" shutdown="SHUTDOWN"> <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" /> <Listener className="org.apache.catalina.core.JasperListener" /> <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" /> <Service name="Catalina"> <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" /> <Engine name="Catalina" defaultHost="localhost"> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true" xmlValidation="false" xmlNamespaceAware="false"> </Engine> </Service> </Server> Apache error log: [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.201.10:8009 (10.176.201.10) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.201.10) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.201.10 [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.201.9:8009 (10.176.201.9) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.201.9) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.201.9 [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.219.168:8009 (10.176.219.168) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.219.168) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.219.168 [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state Load balancer top info: top - 23:44:11 up 210 days, 4:32, 1 user, load average: 0.10, 0.11, 0.09 Tasks: 135 total, 2 running, 133 sleeping, 0 stopped, 0 zombie Cpu(s): 0.1%us, 0.2%sy, 0.0%ni, 99.2%id, 0.1%wa, 0.0%hi, 0.1%si, 0.3%st Mem: 524508k total, 517132k used, 7376k free, 9124k buffers Swap: 1048568k total, 352k used, 1048216k free, 334720k cached Tomcat top info: top - 23:47:12 up 210 days, 3:07, 1 user, load average: 0.02, 0.04, 0.00 Tasks: 63 total, 1 running, 62 sleeping, 0 stopped, 0 zombie Cpu(s): 0.2%us, 0.0%sy, 0.0%ni, 99.8%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 2097372k total, 2080888k used, 16484k free, 21464k buffers Swap: 4194296k total, 380k used, 4193916k free, 1520912k cached Catalina.out does not have any error messages in it. According to Apache's server status, it seems to be maxing out at 143 requests/sec. I believe the servers can handle substantially more load than they are, so any hints about low default limits or other reasons why this setup would be maxing out would be greatly appreciated.

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• Windows Server 2003 - Handling hundreds of simultaneous downloads

  - by Paul Hinett

  At the moment I have a single server with 4 1TB hard disks, daily I haver over 150 MP3 music files uploaded (around 80mb each). At busy periods there is over 300 people streaming / downloading these mixes all at once, 75% of the activity is on the most recently uploaded stuff which is all on a single hard disk. My read speads on the hard disk are very low due to such high activity of 200+ reads all happening at the same time on a single hard disk (ran some tests with HDTach). What would be a logical solution to solve this, a couple of ideas I had are: Load balance with another server Install faster hard disks (what are best these days? SCSI / SATA) Spread the most accessed files over the 4 drives so it is sharing the load between all 4 disks, instead of all the most accessed (most recent) all on the most recently installed drive. Obviouslly load balance is the most expensive option, but would it dramatically help? Some help on this situation would be great!

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